Conventional knee-ankle orthoses have been used for many years in the management of patients afflicted with lower-extremities instabilities. Due to its construction, the conventional knee-ankle orthosis maintains the leg in extension during gait and contributes to an increase in postural lumbar lordosis and thoracic kyphosis. This conventional form of orthosis is still currently prescribed for Duchenne muscular dystrophy patients at the latter stage of their precarious ambulatory period.
Gait analysis shows that the vertical hip oscillation of a Duchenne muscular dystrophy patient increases around 65% with the conventional braces, as compared to hip oscillation without the braces. Observation of the brace patient's gait show that, to perform a walking step, he has to swing forward and upward both his hip and the extended leg while his whole weight is borne by the other leg.
Observation further shows that the lateral trunk sway (i.e. the angle subtended by a straight line joining the neck to the hip joint and the vertical, during a gait cycle) of the conventionally braced patient has a range more than twice that of the unbraced patient. This can be explained again by the lack of knee flexion.
Furthermore, while standing in the braces the patient usually takes an arched position, leaning back his shoulders and bringing his hips forward. This increases the patient lumbar lordosis and thoracic kyphosis.
All of these conditions are related to the fact that the conventional knee-ankle orthoses are rigid static devices primarily designed to support the legs. They provide very limited assistance to the patient in his gait.
Prior art developments are exemplified by U.S. Pat. No. 3,026,869, issued Mar. 27, 1962, U.S. Pat. No. 1,851,241, issued Mar. 29, 1932 and U.S. Pat. No. 3,826,251, issued July 30, 1974.